1. Field of the Invention
The present invention relates generally to coaxial electrical connectors used to transmit microwave radio frequency electrical signals, and more particularly, to microwave coaxial connectors capable of handling relatively higher-power microwave signals.
2. Description of the Relevant Art
Coaxial connectors used to transmit radio frequency signals for broadband telecommunications, military avionics, and microwave systems are well known in the art. Such connectors are often known as “SMP” connectors, or “SMPM” connectors, and are constructed in accordance with military standard MILSTD 348. For example, for many years, Gilbert Engineering Co., Inc. of Glendale, Ariz., now Corning Gilbert Inc., has made available microwave coaxial connectors sold under the trademarks “GPO” and “GPPO” to facilitate so-called “push-on” interconnects in microwave applications. Such connectors are typically designed to handle signals in the frequency range from approximately 2 GHz up to as much as 40 GHz.
One common type of such coaxial connectors is referred to as a “blindmate interconnect”, or “bullet”, having two opposing female ports at its opposing ends. Such a bullet is often inserted between two panel or circuit mounted male ports, also known as “shrouds”, for connecting two modules together; a blindmate interconnect, or bullet, accommodates increased misalignment between two adjacent panel modules while achieving reliable interconnection between the respective ports on such panel modules. Such connectors are relatively small in size, typically measuring less than 10.2 mm (0.40 inch) in length, and only approximately 3.3 mm (0.13 inch) in diameter, to allow for high packing densities. These blindmate interconnects include a center metallic conductor, an outer tubular metallic conductor, and an electrically-insulative dielectric interposed between the center conductor and the outer tubular conductor. The ends of the center metallic conductor are typically formed into resilient, spring-like slotted fingers for gripping a received center conductor of a mating male port. While such slotted fingers are usually plated with gold to reduce contact resistance, there is always some finite amount of contact resistance (typically, about 6 milliohms) at the point at which such slotted fingers grip the center conductor of the mating male port.
In view of their relatively small physical size, such commercially available microwave coaxial connectors necessarily impose limitations in power level of radio frequency signals that can be transmitted by such connectors. Moreover, power level limitations impose corresponding limitations upon the distances over which such RF signals can be transmitted. The power loss of a given RF signal within a connector is a function of the frequency; the higher the frequency, the higher the power loss. In view of the finite contact resistance mentioned above at the point at which the slotted fingers grip the center contact of the male ports mated therewith, a fraction of the power in the radio frequency signal that is transmitted by such coaxial connectors is converted to heat, thereby raising the temperature of the center conductor within such coaxial connectors. The power handling capability of such known coaxial connectors is determined by the cross-sectional size of the center conductor and the amount of contact resistance. Increasing the diameter of the center conductor can increase power handling capability, but the overall size of the connector would also increase, and packing density would decrease. As power increases, temperature rises, and eventually the relatively-small coaxial connector is unable to reliably handle such higher temperatures. In particular, such elevated temperatures cause the dielectric to deteriorate, thereby causing an increase in electrical mismatch, which in turn, causes more power to be reflected back through the connector. Elevated temperatures also degrade and oxidize the spring metal core of the slotted fingers of the center conductor.
Common PTFE (polytetraflouroethylene), also known under the brand name TEFLON®, is the dielectric material ordinarily used within such blindmate interconnects. U.S. Pat. No. 5,067,912 to Bickford, et al. discloses the use of PTFE as an insulator within a microwave connector. Common PTFE is relatively pliable and can be temporarily compressed without being damaged. This property of PTFE is often used to advantage by manufacturers of coaxial connectors during the assembly process; such common PTFE insulators can be press-fit over center conductors and/or press-fit into tubular outer conductors during assembly without causing damage to such insulator. Nonetheless, common PTFE is a relatively poor conductor of heat; it has a thermal conductivity of only 0.25 W/(m-° K) (1.7 BTU-in/(hr.-ft.2-° F.)). As a result, heat added to the center conductor of a conventional blindmate interconnect is not easily dissipated. In addition, common PTFE has a relatively high coefficient of thermal expansion (CTE) value. Accordingly, heat transferred by the center conductor to the surrounding dielectric causes a change in the physical dimensions of the PTFE dielectric. This induced change in physical dimensions of the dielectric again causes electrical mismatch, increased power reflection back through the connector, and even greater heating within the connector.
Accordingly, it is an object of the present invention to provide a coaxial connector for microwave applications wherein the power level of radio frequency signals that can be reliably passed through such connector is significantly increased.
It is a another object of the present invention to provide such a coaxial connector which allows for greater transmission distances by facilitating the transmission of RF signals having greater power levels.
It is still another object of the present invention to provide such a coaxial connector which handles greater power levels without significantly lessening the packing density of such connectors.
It is a still further object of the present invention to provide such a coaxial connector which can be assembled in a relatively simple manner without damaging the dielectric insulator.
Still another object of the present invention is to provide such a coaxial connector wherein the center conductor is reliably captured within the dielectric insulator, and wherein the dielectric insulator is reliably captured within the tubular outer conductor body.
These and other objects of the invention will become more apparent to those skilled in the art as the description of the present invention proceeds.